The invention relates to power management in a computer system.
Power management has become very important in the computer industry, particularly for portable computers, such as laptop units. The industry has developed several power management standards, including the Advanced Power Management (APM) Specification, version 1.2, published by Intel Corporation and Microsoft Corporation in February 1996, and the Advanced Configuration and Power Interface (ACPI) Specification, version 1.0, published in February 1998 by Intel Corporation, Microsoft Corporation and Toshiba K.K. The ACPI Specification, for example, defines several reduced-power states for a computer system, including the xe2x80x9cS3xe2x80x9d, or xe2x80x9cSuspend-to-RAMxe2x80x9d, state and the xe2x80x9cS4xe2x80x9d, or xe2x80x9cSuspend-to-Diskxe2x80x9d, state.
In the ACPI S3 state, the computer removes power from many of its components, including the processor. The states of the processor and other devices in the computer are saved to memory before power is removed. The memory subsystem is powered to retain device and system information. In the S4 state, the computer removes power from all devices, including memory, except for certain devices, such as modems and network interface cards, that must remain powered to recognize signals from external sources. The state of the computer system is saved to a non-volatile, rotating storage device, such as a hard disk, before power is removed.
The S4 state produces more aggressive power savings than the S3 state because the computer does not continue to supply power to system memory. As a trade off, more time is needed to exit the S4 state because the system state information must be restored from a rotating storage medium, for which access time is much greater than the access time associated with random-access memory devices;
A new non-volatile, random-access memory type, known as ferromagnetic or ferroelectric memory, has been developed. Ferromagnetic memory is truly non-volatile in that it retains data for a very long time, i.e., several months or longer, after losing power.
A computer system includes a processor and a non-volatile random-access memory device, such as a ferromagnetic memory device, coupled to the processor. The processor either generates or receives a command to enter a low-power mode. The non-volatile memory device includes a first area reserved for random-access read/write cycles by the processor and a second area reserved for storing processor state information upon entering the low-power mode. The processor and the memory device both are configured to lose power during the low-power mode. In some embodiments, the memory device also serves as a read-only memory device and as a persistent storage device for data and application programs.
Other embodiments and advantages will become apparent from the description and claims that follow.